The proposed research will investigate the development of communication between prelinguistic infants and caregivers to better understand how early social interactions facilitate language learning. The PI's past research has shown that caregivers' contingent responses to prelinguistic vocalizations (i.e. babbling) have both immediate and long-term facilitative effects on infants' speech and language development. Despite the importance of early caregiver responses for infant learning, the characteristics of infant vocalizations that influence caregiver responsiveness are unknown. The proposed studies utilize a playback paradigm, which is a method widely used in studies of animal communication. In a playback paradigm, prerecorded auditory or visual signals are presented to an individual, whose reaction is measured. As applied to human communicative development, caregivers will react to prerecorded audiovisual playbacks of unfamiliar infants' vocalizations and actions. The acoustic qualities of infants' vocalizations will be manipulated to systematically examine their effects on the responses of adults. Project 1 will develop several response measures and validate the playback paradigm as a measure of parental behavior. To assess the validity of the response measures, parents' reactions to the playback stimuli will be compared with their responses to their own infants during play. Next, the playback paradigm will be used to specify the acoustic features of prelinguistic vocalizations that elicit parents' responses. Project 2 will assess the role of caregiving experience on responsiveness. First, adults with varying levels of caregiving experience will be tested in the playback paradigm. The responsiveness of childless adults with high or low levels of caregiving experience will be compared with that of parents with one or multiple children. Project 2 will also examine changes in maternal responsiveness across the birth transition. In many mammals, maternal responsiveness to the acoustic signals of young undergoes dramatic change around the time of birth, but the role of caregiver experience in responding to non-cry prelinguistic vocalizations has yet to be determined. The playback paradigm introduces a new experimental tool for research on early communicative development. By investigating the effects of prelinguistic vocalizations on caregivers' behavior, the proposed studies will improve our understanding of the function of immature sounds in constructing social interactions that facilitate advances in vocal learning. Assessing the ways in which early vocal learning is socially embedded is an important step in understanding the earliest stages of communication and language development. The playback paradigm could eventually be used to improve parent-infant communication in circumstances where early vocal development is disrupted, for example in Down syndrome or autism. By simulating interactions with infants whose vocal development is affected by developmental disorders, the playback paradigm could become a useful intervention tool.